Cytochalasin B (CB) inhibits sugar transport in mammalian cells at low concentrations and affects various forms of cell motility at higher concentrations. We have previously used 3H-CB to reveal high and low affinity CB binding sites in mammalian cells. The high affinity CB binding sites in human red blood cells have been shown to be proteins intimately related to the sugar transport system. In the proposed research, we plan to isolate and characterize the high affinity CB receptors and to recombine them with lipid vesicles to reconstitute an in vitro sugar transport system. To study CB receptors related to cell motility, we shall isolate and characterize low affinity CB binding sites, study the effects of CB derivatives and resin-bound CB on cellular movements, and study the in vitro effects of CB on contractile proteins isolated from muscle and nonmuscle cells. We shall also use the CB binding reaction to study changes in sugar transport activity, motility, microfilament content, and cell growth properties of mammalian cells following viral transformation. The objectives of the proposed research are: (1) elucidation of the molecular basis of action of CB, (2) increasing our knowledge of the cellular components involved in sugar transport and cell motility, and (3) developing CB and its derivatives into useful tools of cell biology and medicine.